For example, Japanese Patent Laying-Open No. 62-1017 (PTD 1) discloses a heating power supply device for heating a negative resistance load. This power supply device includes a power supply transformer and a plurality of thyristor rectifiers connected to the power supply transformer. A load is connected to each of the thyristor rectifiers. The power supply device further includes a semiconductor switch for connecting a plurality of loads to at least one of the plurality of thyristor rectifiers in series, in parallel, or in series-parallel combination.
Furthermore, the configuration for detecting a ground fault in the load connected to the power supply device has also been proposed. For example, Japanese Patent Laying-Open No. 58-175922 (PTD 2) discloses a semiconductor power conversion system having the following configuration. Specifically, the semiconductor power conversion system includes a series path formed of an alternating-current (AC) power supply that supplies an AC output having a frequency different from an output frequency of a semiconductor power conversion device, an element for series resonance that has a frequency of this AC power supply as a resonance frequency, and an impedance element for monitoring a ground current. The series path is interposed between the load of the semiconductor power conversion device and a ground.